#include<conio.h>
#include<stdio.h>
 float Nhap()
 {
 float r;
  
 do  {
           //printf("nhap vao ban kinh duong tron r=");
           scanf("%f",&r);
           }
           while (r<0);
  return r;
 }
main()
{
      float c,s,r;
      printf("nhap bkinh r=");
      r=Nhap();
    //  printf("%f",r=Nhap());
      printf(" chu vi C = %0.2f",2*3.14*r);
      printf("\nn");
      printf(" Dien tich S = %0.2f",r*3.14*r);
 getch();
}
      
